To some extent it is slip on the banana peel humor which is a bit childish but there is a child in all of us. As we get older, people tend to be more cynical of other people. In the range of normal, it isn't abnormal, but not a preferred way in terms of empathy that the best of people have for others. You probably should look into another line of employment interacting less with large numbers of people in a day. It's likely over time, your feelings will get worse.
You seem unhappy with your job, and although tolerating it, retail is typically not high enough a pay scale to be in and unhappy about it.